1. Field of the Invention
The present invention generally relates to an improved end piece for highway crash cushions and other forms of road barriers. The end piece more particularly is configured to trap the bumper or other elements of an impacting vehicle, and to be movable along the barrier. In a preferred form, the end piece resists rolling of a vehicle and acts during the progress of a collision to help decelerate the vehicle from contact velocity to a stop. The end piece is especially useful with highway "turndown" guard rail terminals to help prevent the ramping phenomenon sometimes associated with such terminals. Additionally, the end piece may be used to help control impacts with Advanced Dynamic Impact Extension Module ("ADIEM") terminals. Such terminals are disclosed in U.S. Pat. No. 4,909,661, incorporated herein by reference.
2. Description of the Prior Art
Many existing guard rails have been built to terminate in a curvilinear "turndown" fashion such that a W-beam, box beam or the like structural member tapers down into the ground, thus providing a ramp to eliminate "spearing" tendencies of an otherwise raised end. While the "turndown" end treatments have successfully reduced the danger of a vehicle being penetrated in a head-on collision, it now appears that these end treatments may induce launching of the vehicle and cause it to become airborne for a considerable distance with the possibility of rollover. It is therefore desirable to develop a system of preventing such ramping, especially a system which could be readily retrofitted onto current "turndown" guard rails.
It is also desirable in the case of solid concrete road barriers to reduce the danger of deadly impact forces when vehicles crash against such barriers. Present barrier end treatments, designed for conventional height (typically about 32 inches) standard concrete median barriers ("CMB"), employ modules of crushable material, such as the ADIEM. The focus of such modules has been on cushioning the impact between a colliding vehicle and the solid barriers. In that regard, an alternative barrier design, known as the LP-IV Low Profile Barrier, has recently been developed which provides for a much lower profile than the CMB. The lower profile (preferably about 24 inches) has significant advantages; however, if the overall height of the ADIEM crash cushion system were decreased to about 24 inches or less (as in the low profile barrier application), an impacting vehicle might be expected to ramp on such a cushion or end treatment. Accordingly, there is a continuing need with road barriers for a means which will not only arrest a vehicle but also help to prevent ramping of the vehicle upon colliding with the barrier.